Error loading Yandex Maps, what should I do?

Question

JavaScript

Why, if you do not specify the onload parameter when connecting the Yandex Maps API, then an error occurs:
(index): 621 Uncaught ReferenceError: ymaps is not defined

At the same time, if you specify:
onload=YandexMapRoute

Then everything works.

The essence of the question: how to make maps work without calling a function on onload?

Answer 1

View what is being done in the YandexMapRoute function and do the same, but without calling the function.